A Rapid Method for the Quan- 
titative Estimation of Glu- 
cose in Urine by Fehling's 
Solution. 
BY 
WALTER MENDELSON, M. D., 
LATE INSTRUCTOR IN URINE ANALYSIS AT THE COLLEGE 
OF PHYSICIANS AND SURGEONS, NEW YORK. 
REPRINTED FROM 
Neto ¥orfc jfUctocal Journal 
for July 7, 1888. Reprinted from the New York Medical Journal 
for July 7, 1888. 
A RAPID METHOD FOR THE QUANTITATIVE 
ESTIMATION OF GLUCOSE IN URINE 
BY FEHLING'S SOLUTION, z 
By WALTER MENDELSON, M. D., 
LATE INSTRUCTOR IN URINE ANALYSIS AT THE COLLEGE OF PHYSICIANS AND 
SURGEONS, NEW YORK. 
My object in writing this short paper is to call the at- 
tention of physicians to a method of using Fehling's quan- 
titative determination for glucose in urine, which effects a 
saving of fully one half the time usually required. 
Before getting at the gist of my subject I desire to em- 
phasize a few peculiarities of the behavior of urine to Feh- 
ling's solution, as it is upon the occurrence of these pecul- 
iarities that the rationale of the method I am about to 
describe is based. 
Every one who has critically examined many specimens 
with Fehling's solution will have noticed two striking facts. 
The first of these is that some urines from which sugar can 
by various tests be positively excluded will decolorize the 
solution, and even give it an orange or opalescent-green 
tint. The second is that urines known to contain sugar 
fail to produce a characteristic precipitate with Fehling's 
test, giving instead appearances identical with those just de- 2 
A RAPID METHOD FOR THE QUANTITATIVE 
scribed, or filling the test-tube with a precipitate usually of 
a yellowish-green color, which never turns red and never 
satisfactorily settles to the bottom, and which is, moreover, 
so fine as to pass through most filters. 
The reason for these disturbing variations from the 
classical action of the test, as described in the books, is to 
be found in the fact that urine contains normally two classes 
of bodies, one of which has the power of reducing copper 
oxide, and the other of redissolving such oxide when from 
any cause it has been reduced. Here, then, we have two 
substances of antithetical action, the final result of their 
presence being according as one or the other preponderates 
in quantity. The less sugar the specimen contains, the more 
disturbing these variations become, and it may happen that 
as much as one half of one per cent, of sugar is present 
without a characteristic precipitate being formed. Con- 
centrated high-colored urines are, as a rule, more apt to 
show these peculiarities than dilute, pale urines. Two 
kinds of error are consequently likely: One that traces of 
sugar may be overlooked, the other that traces may be re- 
ported in urines containing none. 
In another paper I propose to show how small quantities 
of sugar may be detected in spite of these disturbances, 
confining myself here only to the discussion of the quanti- 
tative determination by Fehling's solution. 
The non-appearance of the red oxide and its replace- 
ment by a greenish-yellow precipitate, which persists in re- 
maining in suspension for an indefinite length of time in the 
contents of the flask, are common sources of vexation to 
any one whose time is precious. 
To avoid these ditticuliies, the following procedures 
should be employed : 
First, use a flask capable of containing about 250 c. c., 
and, after adding the usual 10 c. c. of Fehling's solution, fill ESTIMATION OF GLUCOSE IN URINE. 
3 
half full of water, or till the solution is of a very pale blue. 
The reaction takes place much better and can be more 
closely observed than when the test solution is used in con- 
centrated form. Secondly, the urine should be well diluted. 
Make a preliminary qualitative test to judge approximately 
of the quantity of glucose present and dilute accordingly. 
One in ten is a convenient strength. This, together with 
the thinning of the Fehling's solution, will insure proper 
dilution of the normal reducing and dissolving substances of 
the urine, and minimize their disturbing action. 
The temptation to use the urine but slightly diluted or 
of full strength when the amount of sugar is small, so as to 
shorten the time necessary in using the burette, is very 
great, but will always be regretted if yielded to, for it gen- 
erally ends in being obliged to undertake the whole analysis 
afresh after wasting considerable time. 
Put the diluted Fehling's solution on to boil while pre- 
paring the dilution of urine and filling the burette. Then, 
when all is ready, in starting the process, allow only a small 
quantity-from one half to one c. c.-to flow from the 
burette before boiling again, removing the flame and allow- 
ing the ebullition to cease each time before adding more. 
Boil hard each time, as this causes the particles of oxide 
to cohere and fall to the bottom more quickly than other- 
wise. 
Even under the most favorable circumstances-that is, 
when a red precipitate appears at once and falls quickly to 
the bottom as the reaction nears completion-a considera- 
ble time must always elapse before the supernatant fluid is 
sufficiently clear to allow the analyst to determine whether 
all the blue color has been discharged or not, especially as 
the fine particles of red oxide, when in suspension, give to 
an otherwise colorless fluid a violet shimmer. This settling 
may be hastened by adding a dash of cold water to the 4 
A RAPID METHOD FOR THE QUANTITATIVE 
contents of the flask; but Munk * has method 
which is probably the greatest the use of 
Fehling's solution since the test was first proposed, and 
which it is the object of this paper to popularize. 
This consists in adding a small quantity of a solution 
of calcium chloride to the mixture in the flask. (Munk 
recommends three to five drops of a 15-per-cent. solution, 
but in practice I simply make a pretty strong solution, and 
use as much as seems needed.) A voluminous, white, curdy 
precipitate is formed, consisting in part of calcium hydroxide 
and in part of calcium tartrate, the latter being less soluble 
in hot than in cold solutions. This precipitate, from its 
curdy, gelatinous nature, carries down with it the impalpa- 
bly fine powder of the copper oxide, and quickly leaves a 
clear supernatant fluid in which the most delicate shade of 
blue is discernible, if present. 
In practice 1 have found the following the best mode of 
procedure: 
If the oxide comes down red in the beginning, I con- 
tinue adding from the burette until the rapid falling of the 
precipitate to the bottom of the flask warns that the reac- 
tion is nearly complete. I then add about ten drops-or 
enough to give a pretty large quantity of precipitate-of 
the calcium-chloride solution. When the precipitate of 
copper is yellowish-green and shows no sign of turning 
red, I add the calcium-chloride solution as soon as I have 
satisfied myself of the latter fact. Great care must be used 
to boil slowly at first, allowing the flame of the burner to 
play gently, with frequent removals, about the bottom of 
the flask until the whole mass gradually boils. If this is 
not done, owing to the character of the precipitate, explo- 
* I. Munk, Virchow's " Archiv," vol. cv (1886), p. 63. I have made 
an abstract of this article, which may be found in the "American Jour- 
nal of the Medical Sciences " for October, 1886, p. 543. ESTIMATION OF GLUCOSE IN URINE. 
5 
sive boiling may occur, and the whole contents of the flask 
be suddenly landed on the ceiling-a monument to precipi- 
tancy for all time! 
When boiling is once under way there is no more dan- 
ger of such an accident occurring, and ebullition should be 
maintained for some minutes before the precipitate is al- 
lowed to settle. Should it be found, after the calcium tar- 
trate with the copper oxide have settled to the bottom, that 
considerable copper still remains in solution to be precipi- 
tated, it will generally be necessary to add from time to time, 
as the urine is run out of the burette, a few drops more of the 
calcium-chloride solution, as the freshly precipitated calcium 
tartrate has greater clarifying powers than that which has 
already been used. Should the amount of precipitate be- 
come finally very large, more water should be added to the 
flask. 
By the use of this method a sugar determination may 
be made in twenty minutes, and several can be done to- 
gether in even less time each ; whereas, under the common 
method, half an hour would be very short and very excep- 
tional, and an hour or more-depending on the nature of 
the specimen-nothing unusual. 
Two years' constant use, embracing specimens of all 
varieties of contrariness, warrants me in heartily recom- 
mending Munk's method to all who have many, or indeed 
any, quantitative determinations to make, and to whom 
time is valuable. 
179 West Seventy-fourth Street. REASONS WHY 
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